Uncertainty has been defined as a lack of information about an event and has been characterized as an aversive state that people are motivated to reduce. The authors propose an uncertainty intensification hypothesis, whereby uncertainty during an emotional event makes unpleasant events more unpleasant and pleasant events more pleasant. The authors hypothesized that this would happen even when uncertainty is limited to the feeling of "not knowing," separable from a lack of information. In 4 studies, the authors held information about positive and negative film clips constant while varying the feeling of not knowing by having people repeat phrases connoting certainty or uncertainty while watching the films. As predicted, the subjective feeling of uncertainty intensified people's affective reactions to the film clips.